1. Field of the Invention
The invention relates to a gas turbine combined cycle or power plant which drives a gas turbine by a combustion gas obtained by blowing a fuel into high pressure air and burning the fuel so as to generate power in the gas turbine. A steam turbine is driven by steam that is generated by recovering heat from an exhaust gas that drives the gas turbine, so as to generate power in the steam turbine. This improves heat efficiency. The gas turbine combined cycle cools compression air discharged from a low pressure compressor before being made into high pressure air by a high pressure compressor, so as to make a drive force of the high pressure compressor driven by the gas turbine small. Heat energy recovered by the cooling is used for driving the steam turbine, thereby further improving the heat efficiency.
2. Description of the Related Art
There has been a conventional gas turbine combined cycled or power plant which drives a gas turbine by a combustion gas obtained by burning high pressure air and a fuel and drives a steam turbine by steam generated by an exhaust gas discharged from the gas turbine.
This gas turbine combined cycle is structured such that the gas turbine, driven by the combustion gas, outputs the drive force for operating a power generator or the like and drives the compressor for generating the combustion gas having a high temperature and a high pressure. The compressor driven by the gas turbine is provided with a low pressure compressor and a high pressure compressor, and compresses introduced ambient air in two steps so as to make high pressure air, and then supplies the air to a combustion device into which fuel is blown so as to generate combustion gas.
That is, the high pressure compressor is structured so as to suck a high temperature compression air, compressed in the low pressure compressor in an adiabatic manner and reaching a temperature of 190.degree. C. or more, and further increase the pressure of the compression air to high pressure air, and then supply the air to the combustion device.
Accordingly, the drive force of the high pressure compressor is increased and much of the drive force generated in the gas turbine is consumed, so that the drive force which the gas turbine can output is reduced. Accordingly, this causes a reduction of efficiency of the gas turbine combined cycle or power plant.
Therefore, there has been employed an intermediate cooling type gas turbine combined cycle or power plant (hereinafter referred to as an intermediate cooling type combined gas turbine cycle or power plant) which is structured so as to cool a high temperature compression air discharged from the low pressure compressor in an intermediate cooling device, and supply the compression air cooled to about 100.degree. C. to a high pressure compressor so as to increase the pressure to of the air to a high pressure. This makes the drive force supplied from the gas turbine for driving the high pressure compressor small so as to improve the magnitude of the drive force supplied by the gas turbine.
FIG. 3 is a systematic view which shows an intermediate cooling type gas turbine combined cycle in accordance with the conventional art.
As shown in the drawing, an intermediate cooling type gas turbine combined cycle or power plant 30 is constituted by a gas turbine portion 10 comprising a power generator 1, a low pressure compressor 2, a high pressure compressor 3, a combustion device 4 (combustor), a gas turbine 5, a rotor cooling cooler 6, cooling towers 7 and 9, and an intermediate cooling device 8. The cooling type gas turbine combined cycle 30 also includes an exhaust gas heat recovery portion 23 comprising a high pressure steam generating device 11, an intermediate steam generating device 12, a low pressure steam generating device 13, a high pressure steam pipe 14, an intermediate pressure steam pipe 15, a low pressure steam pipe 16, a power generator 17, a high pressure steam turbine 18, an intermediate pressure steam turbine 19, a low pressure steam turbine 20, a reheater 21 and a condenser 22.
The high pressure compressor 3, the low pressure compressor 2 and the power generator 1 are coaxially connected to the gas turbine 5 of the gas turbine portion 10, and as mentioned below, the gas turbine 5 is structured so as to drive the compressors via combustion gas so as to transform ambient air A into a predetermined high pressure air for performing a combustion such that power is generated.
At first, the ambient air A is sucked by an intake port of the low pressure compressor 2 driven by the gas turbine 5, compressed in an adiabatic manner and increased to a predetermined low pressure, and then discharged from a discharge port of the low pressure compressor 2 as a high temperature compression air having a temperature equal to or more than 190.degree. C.
When introducing this compression air having a high temperature into the high pressure compressor 3, the drive force of the high pressure compressor 3 required for increasing the pressure of the air is increased, whereby the drive force supplied from the gas turbine 5 for driving the high pressure compressor 3 is also increased such that the drive force for driving the generator 1 is reduced. Thus, the intermediate cooling device 8 having the cooling tower 9 is provided between the discharge port of the low pressure compressor 2 and the suction port of the high pressure compressor 3 so as to cool the compression air discharged from the low pressure compressor 2 to about 100.degree. C. before being introduced into the high pressure compressor 3.
The high pressure air increased by the high pressure compressor 3 is introduced into the combustion device 4, and mixed with a fuel F introduced to the combustion device 4, which is burned so as to produce a combustion gas having a high temperature and a high pressure, whereby the gas turbine 5 is driven in the manner mentioned above.
Further, a part of the high pressure air that is discharged from the high pressure compressor 3, or a high pressure air extracted from a middle step of the high pressure compressor 3 (hereinafter referred to as extracted steam), is cooled to about 200.degree. C. by the rotor cooling cooler 6 and supplied to an inner portion of a rotor blade or a stator blade of the gas turbine 5 that is exposed to the high temperature combustion gas passing within the rotor of the gas turbine 5, thereby cooling the rotor blade or the stator blade from an inner portion thereof.
Still further, the high temperature exhaust gas driving the gas turbine 5, and discharged from the gas turbine 5, is discharged to the ambient air from the chimney 24 via the discharged heat recovery portion 23.
Next, in the exhaust gas heat recovery portion 23, a recovery of the heat from the exhaust gas is performed by successively passing the exhaust gas from the gas turbine 5 through inner portions of the high pressure steam generating device 11, the intermediate pressure steam generating device 12 and the low pressure steam generating device 13, which are arranged in the discharged heat recovery portion 23 so as to respectively generate steam having a high pressure, an intermediate pressure and a low pressure. The steam having the respective pressures is fed to the high pressure steam turbine 18, the intermediate pressure steam turbine 19 and the low pressure steam turbine 20, which are coaxially connected respectively by the high pressure steam pipe 14, the intermediate pressure steam pipe 15 and the low pressure steam pipe 16. The steam expands within the turbines 18, 19 and 20 so as to rotate the respective steam turbines, drive the power generator 17 coaxially connected to the steam turbines, and generate electric energy.
Further, at an outlet of the high pressure steam turbine 18 the exhaust gas driving the high pressure steam turbine 18 is mixed with the intermediate pressure steam generated in the intermediate pressure steam generating device 12 and supplied by the intermediate pressure steam pipe 15. This mixture is heated by the reheater 21 arranged in the exhaust gas heat recovery portion 23, whereby a temperature of this mixture flowing into an inlet of the intermediate pressure steam turbine 19 is increased, such that an output thereof is increased.
Further, at an outlet of the intermediate pressure steam turbine 19, the exhaust gas driving the intermediate pressure steam turbine 19 is mixed with the low pressure steam generated in the low pressure steam generating device 13 and supplied by the low pressure steam pipe 16. This mixture is supplied to the low pressure steam turbine 20.
Still further, at an outlet of the low pressure steam turbine 20, the exhaust vapor gas discharged from the low pressure steam turbine 20 is transformed into water by the condenser 22, which water is supplied to each of the high pressure steam generating device 11, the intermediate pressure steam generating device 12 and the low pressure steam generating device 13.
In the intermediate cooling type gas turbine combined cycle 30 structured in the manner mentioned above, it has been known that the following advantages exist in comparison with the simple gas turbine combined cycle in which a conventional intermediate cooling device is not provided.
(a) It is possible to reduce the power of the high pressure compressor 3 that is required for increasing the pressure of the compression air driven by the gas turbine 5 and compressed by the low pressure compressor 2. The compression air supplied to the combustion device 4 is reduced in temperature at the inlet of the high pressure compressor 3 via the intermediate cooler 8, so that there is an advantage in that the output supplied from the gas turbine 5 to the power generator 1 and the like is increased.
That is, since the power required for the high pressure compressor 3 can be relatively reduced with respect to the output of the gas turbine 5, the power required for the high pressure compressor 3 can be reduced even when the ambient air A is of a high temperature, such that there is an advantage in that a reduction of an efficiency of the gas turbine 5 can be restricted.
(b) Further, also in the conventional simple gas turbine combined cycle, the high pressure air extracted from the high pressure compressor 3 is used for cooling the high temperature portion of the rotor blade, the stator blade and the like of the gas turbine. However, in the intermediate cooling type gas turbine combined cycle, since the temperature of the air at the inlet of the high pressure compressor 3 is reduced by the intermediate cooling device 8, and the high pressure air exiting from the high pressure compressor 3 is cooled by the rotor cooling cooler 6, which air is to be supplied to the high temperature portion of the rotor blade or the stator blade, it is possible to reduce the temperature of the air at the outlet of the high pressure compressor 3, and thereby reduce the temperature of the cooling air used for cooling the high temperature portion of the gas turbine 5, as well as reduce the amount of cooling air flowing from the high pressure compressor 3 via the rotor cooling cooler 6.
This reduction in the amount of cooling air causes a reduction of a mixing loss corresponding to a pressure loss generated when the combustion gas and the cooling air flowing within a turbine gas pass are mixed. This results in an increased efficiency and an increased output of the gas turbine 5, whereby it is possible to increase the output of the gas turbine 5 via an increase in the amount of flow of the high pressure air flowing into the combustion device 4 from the high pressure compressor 3.
(c) Further, it is also possible to increase an efficiency and an output of the gas turbine by reducing the temperature of heat discharged from the rotor cooling cooler 6 to a predetermined air temperature. The heat discharged from the rotor cooling cooler 6 results from using the cooler 6 to reduce the temperature of the extracted air used for cooling the high temperature portion of the gas turbine.
As mentioned above, in accordance with the conventional intermediate cooling type gas turbine combined cycle, there is the advantage that it is possible to increase the gas turbine output and the combined output. However, since the discharged heat from the intermediate cooling device 8 and the rotor cooling cooler 6 is discharged to the ambient air by the cooling towers 7 and 9, the efficiency of the gas turbine 5 is reduced. Further, since the discharged heat from the intermediate cooling device 8 and the rotor cooling cooler 6 has a great disadvantage in that reduction of the efficiency of the exhaust gas heat recovery portion 23 is realized, this intermediate cooling device 8 has not been actually applied to the conventional gas turbine combined cycle.
In this connection, when the compression air discharged from the low pressure compressor 2 at a temperature of at least 190.degree. C. is cooled to about 100.degree. C. by the intermediate cooling device 8 before being supplied to the high pressure compressor 3, the calories discharged from the cooling tower 9 to the ambient air frequently reaches 5 MW. This results in a disadvantage in that the temperature of the high pressure air supplied to the combustion device 4 is reduced, and the efficiency of the gas turbine 5 is also reduced, in spite of the advantages (a) to (c) mentioned above being obtained. Further, there are disadvantages in that the temperature of the exhaust gas from the gas turbine 5 is reduced, the calories recovered by the exhaust gas heat recovery portion 23 is reduced, and the drive force output from the exhaust gas heat recovery portion 23 is also reduced.